Answer:
D. So immigrants could learn about democracy
Explanation:
In the 19th century, there was the reformation of schooling in the US, lead by Horace Mann. With this, common or public schools were promoted as one of the key services of the US. These schools would be funded by tax money and would allow everyone the opportunity to schooling.
One of the main reasons for this was to create educational opportunities for poor people and immigrants who did not have resources. The idea was to help immigrant children to accommodate to American culture and way of living. Democracy was considered one of the main US ideas, and it was considered immigrants need to learn about it in order to adapt to the society and accept their American identity.